1. Field of the Invention
The present invention pertains to heat exchangers of the flat plate type, and in particular to such heat exchangers where a plurality of heat exchange plates are clamped between massive end plates.
2. Description of the Related Art
Heat exchangers are employed in a wide variety of commercial applications. In the food industry, for example, it is important that process equipment be maintained to a high standard of cleanliness. Fluid-type heat exchangers frequently employ a labyrinth of relatively small sized channels (i.e., small compared to the path length) through which the fluid is made to travel. Walls of the heat exchanger are in thermal contact with the fluid flowing therethrough. The heat exchangers are immersed in a heat transfer medium such as the ambient atmosphere, or a forced air flow. The heat exchangers may also be placed in thermal contact with a liquid heat transfer medium, and it is important that the medium be kept out of contact with the food products flowing through the heat exchanger.
In typical food processing operations, and in a variety of other commercial applications it is important that the heat exchanger be thoroughly cleaned between production runs. To aid in such cleaning, flat plate heat exchangers have been developed where the core of the heat exchanger is assembled by stacking an array of heat exchanger plates, forming flow channels between adjacent plates. One example of a plate-type heat exchanger is given in U.S. Pat. No. 4,162,703. The heat exchanger plates are arranged in a stack, and first and second fluids are passed through the stack, for thermal transfer between the fluid flows.
In order to prevent leakage from the flow channels, or intrusion of heat transfer medium therein, the plates are pressed together with a pressure sufficient to form a seal therebetween. Frames have been provided with a pair of opposed end plates, or pressure plates which are clamped together, and which receive the stack of heat transfer plates therebetween. The pressure plates may be drawn together, for example, by a threaded shaft which is readily loosened to permit disassembly of the heat exchanger plates, for their thorough cleaning after a production run.
U.S. Pat. No. 4,813,478 issued to Jonsson, et al., on Mar. 21, 1989 discloses a heat exchanger apparatus wherein a stack of heat exchanger plates are sandwiched between a pair of relatively plates are sandwiched between a pair of relatively massive end plates. Fastening means such as a threaded shaft extending between the pressure plates compresses the stack. The heat exchanger plates have generally rectangular major surfaces, and are elongated in a vertical direction. Generally rectangular openings are formed in the upper and lower edges of the heat exchanger plates, being centrally located in those edges, midway between the lateral (vertical sides of the plates). A rectangular bar extends between the pressure plates and is received in the openings of each plate in the stack to provide an alignment for the plates in the stack.
Various heat exchangers have been constructed having a frame or outer casing for holding a heat transfer core comprised of an assembly of heat exchanger plates. Such arrangements are generally disclosed in U.S. Pat. Nos. 4,095,646, issued June 20, 1978 to Granetzke; 4,301,863 issued Nov. 24, 1981 to Bizzarro; 4,384,611 issued May 24, 1983 to Fung; 4,609,039 issued Sept. 2, 1986 to Fushiki, et al., and 4,762,171 issued Aug. 9, 1988 to Hallstrom, et al.
U.S. Pat. No. 4,090,556, issued to Almqvist, May 23, 1978 also discloses a flat plate heat exchanger with generally rectangular plates having cutouts in the upper and lower edges thereof. The cutouts include a rectangular recess for receiving a horizontal flange of an upper hanger member which is generally T-shaped in cross-section. The cutouts are formed such that plate material is disposed above the horizontal flange of the upper hanger, preventing downward displacement of the heat exchanger plate. The cutouts are also formed with a central opening suitable for receiving a lower hanger member which is generally square in cross-section. The top and bottom portions of the heat exchanger plates are mirror images of one another, with the cutouts cooperating with either the upper hanger of T-shaped cross-section or the lower hanger of square cross-section.
U.S. Pat. No. 4,660,633 discloses a plate heat exchanger having plates of two different types clamped together between massive pressure plates. It is important that a fluid-tight seal be formed between adjacent pressure plates when clamped together, and it is known to employ strip-like gaskets of resilient material between pressure plates for this purpose. In a first type of heat exchanger plate, U.S. Pat. No. 4,660,633 provides an open-top channel of generally trapezoidal cross-sectional configurtion. The open top of the channel has a smaller dimension than the base of the channel, so as to hold a gasket captive therein when received in the channel. The open top of the channel permits sealing communication between the gasket and a neighboring heat exchanger plate.
U.S. Pat. No. 4,781,248 also discloses a plate-type heat exchanger employing a resilient gasket for sealing between adjacent plates. As with the plates of U.S. Pat. No. 4,660,633 the plates of U.S. Pat. No. 4,781,248 have four circular openings, one at each corner thereof, in addition to medially located top and bottom openings for receiving a hanger bar. Conduits are passed between the circular openings of the heat exchanger plates and provide alignment for the plates in the stack, a convenient feature for those heat exchangers having conduits passing therethrough.
U.S. Pat. No. 4,592,414 also
discloses a heat exchanger plate having four openings therein for fluid passage, one at each corner of the plate. Raised ribs are formed at each opening. Pairs of heat exchanger plates are bonded together such that the raised ribs extend in opposing outward directions. When placed together in a stack, the raised ribs are brought into contact with one another. As mentioned, the raised ribs are provided in pairs at each end of the heat exchanger plate. One raised rib of each pair has an outwardly protruding wall and the other raised rib of the pair has an opening formed therein. When the heat exchanger plates are stacked together, the outwardly extending wall of one plate assembly is received in the opening of an opposing plate assembly, and thus the plate assemblies are interfitted one in another. U.S. Pat. No. 4,285,397 also provides an interfitting between heat exchanger plates, and includes outwardly extending collars received in orifices of an adjacent heat exchanger plate.
U.S. Pat. No. 4,854,382, issued to Funke on Aug. 8, 1989 also discloses a plate heat exchanger with generally rectangular plates having openings at each corner thereof for passage of fluid when the plates are stacked together.
Certain advances are still being sought for heat exchangers, particularly heat exchangers which are routinely disassembled for cleaning and maintenance. It is important, especially in a production environment, that heat exchanger plates which are assembled in a stack are quickly and easily aligned one with another. In order to optimize the heat transfer capacity of a plate, only relatively small areas of the plate are provided for sealing engagement with an adjacent plate, and the heat transfer channels formed by a plate are, typically, numerous and of relatively small cross-sectional dimension. It is important therefore that the channels of one plate be accurately aligned with the channels of another plate and that the sealing surfaces of one plate be accurately aligned with the sealing surfaces of a mating plate if flow is to be confined within the resulting flow channels, as intended.
It is also desirable that the plates of a stack be self-aligning, not requiring significant attention during an assembly process. Further, it would be advantageous if adjacent plates would be self-sealing, making efficient use of the pressure typically applied to a stack of heat exchanger plates of similar size and passageway design.